College students engage in more high-risk, heavy episodic drinking (HED) than non-college peers and older adults. HED can lead to a number of negative effects; yet no studies have examined the impact of high-risk drinking patterns on bone health. Emerging adulthood is a critical developmental period for achieving peak bone mass (PBM). However, pilot research by PI Almstedt indicates an alarming trend among some college students; at a time when students should be gaining BMD, a substantial number of students are maintaining or losing BMD. Even small reductions (1%-3%) in bone mineral density (BMD) can have lifelong detrimental effects on osteoporosis risk and future fracture. Our preliminary research indicates that these observed trends in BMD cannot be explained by dietary factors (e.g., calcium intake), weight loss, smoking, oral contraceptive use, or physical activity. Research among animal models and non-emerging adult populations indicates that alcohol use may provide a plausible explanation for negative trends in college students' BMD. For example, among older adults low-to-moderate alcohol use may have positive effects; however, heavy and chronic drinking can negatively impact bone health. The proposed study extends these previous findings by examining the relationship between HED and bone health in college students in order to reveal a potentially serious long- term health consequence of HED during this critical developmental period. This proposal looks longitudinally at 180 college students over the course of one year. Analyses will include assessments of alcohol use, diet and physical activity, bone scans using state-of-the-art dual energy x-ray absorptiometry (gold standard measure of BMD), and blood assays for biomarkers of bone formation and resorption (i.e., BAP and DPD) at three time points over 12 months. In addition, participants will complete monthly self-reports of alcohol use and regular assessment of physical activity. The main study outcomes will consist of changes in left hip, posterior-anterior lumbar spine and lateral lumbar spine BMD. Alterations in BAP and DPD biomarkers of bone metabolism will be explored to help explain mechanisms for the changes in BMD. Given that males typically reach their PBM later than females, we will examine sex as a possible moderator of the effects of HED on BMD. Furthermore, as physical activity can be a protective factor for bone health, we will assess this as a potential moderator. Age of alcohol initiation will also be examined as a moderator to test whether college alcohol use is more or less detrimental for bone health among those who drink at an earlier age. This exploratory study aligns well with the R21 mechanism by extending biomedical alcohol and bone research in a new direction by targeting a high- risk and developmentally important group. This study could have major implications for understanding the long-term health consequences of college alcohol use on bone health and for interventions aimed at mitigating the potential harm to skeletal health evidenced in this work (e.g., diet or exercise programs).